1. Field of the Invention
The present invention relates to a steering wheel that is light in weight and is provided with a moment of inertia that is necessary for steering wheels.
2. Description of the Related Art
Hitherto, it has been required to reduce the weight of a steering wheel as a part of reducing the weight of a vehicle in order to improve fuel consumption, etc. In view of this, there is proposed a steering wheel having a core member made by die casting of a light-weight alloy such as magnesium alloy (see Japanese Patent Application Laid-open Publication 10-203376). Furthermore, there is proposed a steering wheel core member made of a fiber-reinforced plastic (FRP) (see Japanese Patent Application Examined Publication 6-98712).
On the other hand, a steering wheel is also required to be high in moment of inertia.
Thus, in case that a steering wheel is made to be simply light in weight, its moment of inertia becomes too low. This may cause the steering wheel to have some problems. For example, it is pointed out in Japanese Patent Application Examined Publication 6-98712 that a light-weight steering wheel having an FRP core member tends to have a problem of circumferential vibration. To solve this problem, it is proposed therein to increase the weight of a rim portion of the steering wheel by winding a high specific gravity fiber (e.g., a metal wire) around the rim portion. This proposal, however, inevitably increases the steering wheel production cost, due to the necessity of additional facilities and the increase of the production steps.
Furthermore, there is a process of producing a conventional steering wheel (see FIGS. 3 and 4) by provisionally fixing an iron insert mass “c” to a rim portion of a core member “b” with an aluminum tape “d” and then by covering the rim portion with a normal polyurethane resin covering “e” having a specific gravity of less than 0.6. This iron insert mass “c” is used for increasing the weight of the rim portion. This process is also disadvantageous in terms of production cost, due to the increase of the parts and the production steps.